There are many situations where it is necessary to fasten together components of a structure or apparatus which are to be used in an environment which is susceptible to vandalism or unauthorised tampering. The present security screw has been devised particularly for use in fastening components such as street signs, banner arms and other fittings to roadside poles or other similar installations. It is envisaged however that a security screw of this type has a much wider application such as the fastening of window locks or door locks or in any other situation where a screw type fastener must be secured by an authorised user while yet remaining difficult or impossible to release by an unauthorised user.